3d intraoral scanner measuring fluorescence

ABSTRACT

A 3D scanner system for detecting and/or visualizing cariogenic regions in teeth based on fluorescence emitted from said teeth, the 3D scanner system including data processing means configured for mapping a representation of fluorescence emitted from the teeth onto the corresponding portion of a digital 3D representation of the teeth to provide a combined digital 3D representation.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.16/512,583, filed on Jul. 16, 2019, which is a continuation of U.S.application Ser. No. 16/283,020, filed on Feb. 22, 2019, now U.S. Pat.No. 10,905,333, which is a continuation of U.S. application Ser. No.16/264,835, filed on Feb. 1, 2019, now U.S. Pat. No. 11,246,490, whichis a continuation of U.S. application Ser. No. 14/411,160, filed on Dec.24, 2014, now U.S. Pat. No. 10,238,296, which is a U.S. national stageof International Application No. PCT/DK2013/050213, filed on Jun. 27,2013, which is claims priority from U.S. Provisional Application No.61/665,015, filed on Jun. 27, 2012 and Danish Application No. PA 201270382, filed on Jun. 29, 2012. The entire contents of each of U.S.application Ser. No. 16/512,583, U.S. application Ser. No. 16/283,020,U.S. application Ser. No. 16/264,835, U.S. application Ser. No.14/411,160, International Application No. PCT/DK2013/050213, U.S.Application No. 61/665,015, and Danish Application No. PA 2012 70382 arehereby incorporated herein by reference in their entirety.

TECHNICAL FIELD

The invention relates to intraoral 3D scanning. In particular theinvention relates to a 3D scanner system where fluorescence recordedfrom a patient's teeth is used for detecting cariogenic regions on theteeth. In particular the invention relates to a 3D scanner system wherefluorescence recorded from the intraoral cavity is used when generatinga digital 3D representation of the intra oral cavity.

BACKGROUND

US 2008/0063998 describes a technique wherein one fluorescence image andone reflectance image are combined to form an image in which thecontrast between a cariogenic region and a sound tooth structure isheightened in the 2D image.

US 2008/094631 describes a system with intraoral camera and measuringdevice. The measuring device is capable of collecting color,translucency, fluorescence, gloss, surface texture and/or other data fora particular tooth from the measuring device which then may be combinedwith images captured by intraoral camera.

Optical 3D scanners for recording the topographic characteristics ofsurfaces within the intraoral cavity, particularly of the dentition, areknown in the prior art (e.g., WO 2010/145669). Examples of commerciallyavailable 3D intraoral scanners are 3Shape TRIOS, Cadent iTero, SironaCerec, and 3M Lava C.O.S.

The size of any probe element in intraoral scanners is limited becauseit has to fit into the human mouth. Accordingly, the field of view ofsuch scanners is smaller than the object of interest in manyapplications, which can be multiple neighboring teeth or an entiredental arch. Hence, intraoral 3D scanners rely on “stitching” severalsub-scans, each representative of a field of view, but obtained inmultiple positions, e.g., by moving the 3D scanner along the dentalarch. The 3D scanner records a series of sub-scans that are to bestitched to yield an overall digital 3D representation of the surfacetopography for the scanned part of the intraoral cavity. A sub-scanrepresents a depth map for a given relative position and orientation ofthe 3D scanner and the patient's intraoral cavity. To obtain multiplesub-scans, the 3D scanner is moved along the intraoral cavity or someregion thereof and potentially also angled differently. The 3D scanneris to be moved and angled such that at least some sets of sub-scansoverlap at least partially, in order to enable stitching. The result ofstitching is a digital 3D representation of a surface larger than thatwhich can be captured by a single sub-scan, i.e., which is larger thanthe field of view of the 3D scanner. Stitching, also known asregistration, works by identifying overlapping regions of 3D surface invarious sub-scans and transforming sub-scans to a common coordinatesystem such that the overlapping regions match, finally yielding theoverall scan. The Iterative Closest Point (ICP) algorithm is widely usedfor this purpose.

SUMMARY

It is an object of the invention to provide a 3D scanner system which iscapable of mapping fluorescence and/or a representation of a cariogenicregion onto a digital 3D representation of the teeth.

It is an object of the invention to provide a 3D scanner system whereinthe same image sensor is used for recording the probe light reflectedfrom the teeth and the fluorescence emitted from fluorescent materialsof the teeth, such as fluorescent materials in cariogenic regions of atooth.

It is an object of the invention to provide a 3D scanner system whereinprobe light reflected from the teeth and fluorescence emitted fromfluorescent materials of the teeth, such as fluorescent materials incariogenic regions of a tooth, can be read from the same recorded image.

Disclosed is a 3D scanner system for detecting and/or visualizingcariogenic regions in teeth based on fluorescence emitted from saidteeth, said 3D scanner system comprising:

-   -   an illumination unit capable of providing probe light for        illuminating the teeth, where said probe light comprises light        at a first wavelength which is capable of exciting a fluorescent        material of the teeth;    -   an image sensor for recording images of light received from the        illuminated teeth, where said image sensor is capable of        detecting fluorescence emitted from said fluorescent material        when this is excited by light at said first wavelength;    -   data processing means configured for:        -   i. creating a digital 3D representation of the 3D topography            of the teeth based on recorded images comprising probe light            reflected from the teeth;        -   ii. creating a representation of the fluorescence emitted            from the fluorescent material of the teeth based on recorded            images comprising the emitted fluorescence, and        -   iii. mapping the representation of the emitted fluorescence            onto the corresponding portion of the digital 3D            representation of the teeth to provide a combined digital 3D            representation; and    -   a visual display unit on which the combined digital 3D        representation is visualized.

In the visualization of the combined digital 3D representation thefluorescence and/or cariogenic regions are arranged according to theirtrue position on the teeth. In some cases, caries can be detecteddirectly from the fluorescence emitted from the cariogenic region whenilluminated by light at the first wavelength, such that therepresentation of the emitted fluorescence is a direct representation ofthe cariogenic region.

The mapped representation of an identified cariogenic regions mayprovide an improved visibility in relation to the tooth surface comparedto how visible the identified cariogenic regions are on the tooth, suchthat the visualization of the combined digital 3D representation canprovide valuable assistance to the dentist when examining a patient'sset of teeth. This may e.g., be the case when the cariogenic region isrepresented with a distinct color and/or brightness in the combineddigital 3D representation.

In the context of the present invention, the phrase “recordingfluorescence” may refer to the case where fluorescence images showingfluorescence emitted from the fluorescent material are recorded.

The 3D scanner system according to the present invention has anillumination unit with at least a first light source that can emit lightat a first wavelength intended to excite fluorescence materials in partsof the intraoral cavity, and an image sensor that can measure thefluorescence emitted from the fluorescent material when illuminated withlight at said first wavelength. In some embodiments, the first lightsource provides UV light, and the fluorescence emitted from thefluorescent material in the hard dental tissue has a wavelengthcorresponding to visible light, such that standard image sensors can beused in the invention. Light sources useful in this invention can belasers or LEDs, or other.

A digital 3D representation of the 3D surface topography of an intraoralcavity can be generated based on light reflected from surfaces of theintraoral cavity. When a surface of the intraoral cavity is illuminatedwith light from a light source of the 3D scanner system the lightreflected from the surface within a field of view is detected by animage sensor of the 3D scanner system. Based on the reflected light thedata processing means can compute a sub-scan for the region of thesurface arranged within the field of view. A series of sub-scans can becomputed when e.g., a handheld part of the 3D scanner system is movedrelative to the intraoral cavity such that different regions of thesurface are arranged in the field of view.

The fluorescence emitted from the hard dental tissue may have a spectraldistribution which depends on the wavelength of the light used to excitethe fluorescent material, such that the fluorescence predominantly iswithin one wavelength range for one value of the first wavelength andwithin another wavelength range for another value of the firstwavelength. The fluorescence may be emitted over a fluorescencewavelength range in which the fluorescent material emits fluorescencewhen excited by light at said first wavelength.

For measuring the 3D topographic characteristics of one or more surfacesof the intraoral cavity, the 3D scanner can employ any of the opticalprinciples known in the art, e.g., focus scanning, confocal scanning,triangulation, or others. All these principles require at least onelight source and measure some characteristic of the light reflected fromthe intraoral surface.

The image sensor is configured for recording the fluorescence emittedfrom the hard dental tissue when illuminated by light at the firstwavelength, i.e., the image sensor allows the detection light at leastat a wavelength which is larger than the first wavelength.

In some embodiments, the recording of the 3D topographic characteristicsof utilizes reflections of the light at said first wavelength from thesurfaces of the intraoral cavity. Some of the light at the firstwavelength is reflected from the surfaces of the intraoral cavity whilesome is absorbed by fluorescent materials in the hard dental tissue.

In some embodiments, the image sensor is capable of detecting light atsaid first wavelength, such that the image sensor can detect both thefluorescence and light at the first wavelength. In this case, the imagesensor can in addition to recording fluorescence from the hard dentaltissue also be used for recording light at the first wavelengthreflected from the surfaces of the intraoral cavity. The sub-scans forthe surface can then be computed based on the recorded light at thefirst wavelength. The fluorescence and the reflected light can bedistinguished either by the data processing means or by an opticalfilter. In the data processing means of a 3D scanner system utilizing afocus scanner configured for projecting a pattern of light onto theintraoral cavity surface, the fluorescence and the reflected light canbe distinguished by a decomposition of the intensities recorded by theimage sensor into the corresponding components.

In some embodiments, the fluorescence and the reflected light aredistinguished by using an image sensor comprising a color filter array,such as a Bayer color filter array, and selecting the illumination unitsuch that it only provides probe light at a first wavelength in the bluepart of the optical spectrum (e.g., at 405 nm). The blue pixels of theBayer filter then allows reflected probe light to be recorded while thered and/or green pixels allows emitted fluorescence to be recorded suchthat the reflected probe light and the fluorescence can be recorded inthe same image. The data processing means are then configured forreading the blue pixels on the recorded image only for creating thedigital 3D representation of the teeth, and for reading the red/greenpixels only for creating the fluorescence representation.

In some embodiments, the recording of the 3D topographic characteristicsof the surface involves light at a second wavelength. The secondwavelength may be such that light at the second wavelength mainly isreflected from the surfaces of the intraoral cavity with only a smallfraction being absorbed by fluorescent materials in the hard dentaltissue.

In some embodiments, the probe light comprises light at a secondwavelength and the image sensor is capable of detecting light at saidsecond wavelength, and where the digital 3D representation of the teethis created based on light at the second wavelength in said imagescomprising probe light reflected from the teeth.

The absorption coefficient of the probe light in the teeth material maybe 10 times weaker at the second wavelength than the first wavelength,such as 100 times weaker, such as 500 times weaker.

In some embodiments, the illumination unit is configured for providinglight at the second wavelength for use in recording 3D topographiccharacteristics of the surface.

In some embodiments, the image sensor is capable of detecting light atsaid second wavelength, such that the image sensor can detect both thefluorescence and light at the second wavelength. In this case, the imagesensor can in addition to recording fluorescence from the hard dentaltissue also be used for recording light at the second wavelengthreflected from the surfaces of the intraoral cavity. The sub-scans forthe surface can then be computed based on the recorded light at thesecond wavelength.

In some embodiments, the wavelength of the emitted fluorescence issimilar or identical to that used for recording the 3D topographiccharacteristics, such as similar or identical to the second wavelength.This is advantageous because the optical design can be simple, withlittle or no need to compensate for chromatic aberration.

An image sensor which is capable of detecting light at two differentwavelengths and distinguishing between the two wavelengths can berealized by arranging a filter in front of the photodetectors of theimage sensor, where some regions of the filter allows light at onewavelength to pass while other regions allow light at the otherwavelength to pass. One configuration of such a filter could be amodified Bayer filter adapted to allow, e.g., light at the firstwavelength to pass to one known group of photodetectors and thefluorescence to pass to another known group of photodetectors in theimage sensor.

In some embodiments, the 3D scanner system comprises a further imagesensor.

In some embodiments, the further image sensor is configured fordetecting light at said first wavelength.

In some embodiments, the further image sensor is configured fordetecting light at a second wavelength.

The image sensor or image sensors are arranged to capture light receivedfrom tissue of the intraoral cavity arranged within a field of view. Thefield of view is to some extent determined by the image sensor and theoptical system of the 3D scanner system.

In some embodiments, the image sensor is configured for detecting lighta wavelength range of 400 nm to 850 nm, such as in a range of 500 nm to750 nm.

In some embodiments, the further image sensor is configured fordetecting light within a wavelength range of 500 nm to 850 nm.

In some embodiments, the image sensor comprises an array of sensorelements, where at least a portion of the sensor elements are capable ofdetecting the emitted fluorescence.

This may e.g., be realized by using a color image sensor with a colorfilter array, such as a Bayer filter.

In some embodiments, the image sensor comprises a 2-dimensionaldetector, such as a 2D array of sensor elements.

In some embodiments, the image sensor comprises a 1-dimensionaldetector, such as a 1D array of sensor elements, and sweeping opticsconfigured for imaging different portions of a surface onto thissubstantially 1-dimensional sensor element.

In some embodiments, the image sensor comprises a single sensor elementand sweeping optics configured for imaging different portions of asurface onto this substantially 0-dimensional sensor element.

In some embodiments, the illumination unit is arranged to illuminatesurfaces within the field of view, such that soft and hard dental tissueof the intraoral cavity of the intraoral cavity arranged within at leastpart of the field of view is illuminated. The illumination unit may beconfigured to illuminate surfaces covering an area which is part of thefield of view, to illuminate surfaces covering an area substantiallyidentical to the field of view, or to illuminate surfaces covering anarea extending beyond the field of view.

In some embodiments, the illumination unit provides light in a firstwavelength range, where said first wavelength is within said firstwavelength range.

In some embodiments, the illumination unit further provides light in asecond wavelength range, where said second wavelength is within saidsecond wavelength range.

In some embodiments, the illumination unit comprises a first lightsource configured for providing said light at the first wavelength, suchas configured for providing in a first wavelength range.

In some embodiments, the image sensor is capable of detecting light atsaid first wavelength, and wherein the digital 3D representation of theteeth is created based on light at the first wavelength in said imagescomprising probe light reflected from the teeth. In such cases theoptical system of the 3D scanner system is designed to allow light atthe first wavelength reflected from the teeth to be collected and guidesto the image sensor.

In some embodiments, the color image sensor comprises a color filterarray comprising a number of filters allowing light at said firstwavelength to pass and a number of filters allowing the emittedfluorescence to pass, and where the data processing means bases at leastpart of the creating of the digital 3D representation of the teeth andat least part of the creating the representation of the fluorescence onthe same recorded images.

In some embodiments, the multichromatic light source comprises amulti-die LED with an array of diodes emitting probe light at differentwavelengths, such as an array of red, green, and blue diodes.

In some embodiments, the illumination unit is capable of selectivelyactivating only the subset of the LED diodes of the multi-die LEDcorresponding to the first wavelength while the image sensor only orpreferentially reads out those pixels in the image sensor that havecolor filters at least approximately matching the color of the emittedfluorescence.

The subset of the dies preferably comprises one or more LED diodes whichemits light at the first wavelength, which is within the excitationspectrum of the fluorescent teeth material, such as an ultraviolet, ablue, a green, or a yellow LED diode depending on the excitationspectrum of the fluorescent material.

In 3D scanner system comprising an illumination unit comprising an arrayof red, green, and blue diodes, and an image sensor comprising a Bayerfilter, the blue diodes of the illumination unit may be selectivelyactivated during the fluorescence measurement, while the image sensoronly reads the pixels that has color filters relating to green and/orred light. The light emitted from the subset of LED dies can then excitethe fluorescent materials in the teeth and the scanner can record thefluorescence emitted from these fluorescent materials.

In some embodiments, the illumination unit is a single light source unitwith only the first light source arranged to illuminate a surface of anintraoral cavity. In such cases the first light source is configured forproviding light which can excite fluorescent material in the hard dentaltissue and which can be reflected from the surfaces of the intraoralcavity such that sub-scans can be computed based in the reflected light.The emission spectrum of the first light source in such a single lightsource unit may be predominantly below 500 nm.

In some embodiments, the emission spectrum of the first light source ispredominantly below 500 nm; the image sensor is capable of detectinglight at said first wavelength, and the data processing means areconfigured for computing said sub-scans for the intraoral cavitysurface/set of teeth from the detected light with said first wavelength,and for creating a digital 3D representation of the intraoral cavitysurface/set of teeth by stitching said sub-scans. This allows for asingle-light-source configuration where the first light source is usedfor both recording the 3D surface topography and the fluorescence.

In some embodiments, the illumination unit of the 3D scanner system onlyhas a single light source, i.e., the first light source, and a filterconfigured for filtering the first wavelength used to excitefluorescence. This filter is arranged such that light received from thefield of view must pass through the filter when propagating to the imagesensor. One way to realize a filtering means is a dedicated opticalfilter, possibly one that can be moved into and out of the beam path.

In some embodiments, the first light source is capable of providinglight at both said first and second wavelengths.

In some embodiments, the illumination unit comprises a second lightsource configured for providing said light at the second wavelength,such as configured for providing in a second wavelength range. Inembodiments with two light sources, with different dominant wavelengths,the second light source is preferably used for recording the 3Dtopographic characteristics and the first light source is used forexciting the fluorescent material in the hard dental tissue.

In such a two-light source configuration, the first and the second lightsources may be arranged at separate positions in the 3D scanner system.That is, the components of the illumination unit may be arrangedseparately in the 3D scanner system, such as separately in a handheldpart of the 3D scanner system.

In some embodiments, the first light source is capable of providinglight at both said first and wavelength and at a second wavelength, orthe illumination unit comprises a second light source configured forproviding said light at the second wavelength, such that theillumination unit is configured for providing light both at the firstwavelength and at the second wavelength, while the image sensor iscapable of detecting light at said second wavelength. The dataprocessing means may then be configured for computing said sub-scans forthe intraoral cavity surface/set of teeth from the detected light withsaid second wavelength and for creating a digital 3D representation ofthe set of teeth by stitching said sub-scans.

In some embodiments, the illumination unit is configured to providelight only at the first wavelength or only at the second wavelength atany time.

In some embodiments, the 3D scanner shifts between the two light sourcesrepeatedly such that the surface of the intraoral cavity is illuminatedsuccessively by the light from the first and the second light source.

Tissue in the field of view of the 3D scanner system is then onlyilluminated by at most one of the first light source and the secondlight source at any time.

This can be realized by sequentially turning first and second lightsources on and off, by providing that a first light source sequentiallyemits light at alternating wavelengths, or by blocking, directing, orselecting which of the first and second wavelengths are directed towardsan exit point of the 3D scanner system.

In some embodiments, the 3D scanner system is configured such that onlyat most one of the first light source and the second light sourceprovides light at any time.

In some embodiments, the emission spectrum of said illumination unitand/or of said first light source is predominantly below 500 nm. Thiscan be realized by an illumination unit which comprises only one lightsource whose emission spectrum is predominantly below 500 nm.

In the context of the present invention, an emission spectrum is said tobe below or above a certain wavelength or within a certain range ofwavelengths if a major portion of the light emitted from theillumination unit and/or from the first light source, such as such asmore than 90%, such as more than 99%, or such as more than 99.9% of thelight is below or above this wavelength or within this wavelength range.

In some embodiments, the first wavelength is in the range of 250 nm to500 nm, such as in the range of 350 nm to 450 nm.

In some embodiments, the first light source is LED emitting blue orviolet colored light which can be used for exciting fluorescentmaterials of teeth.

In some embodiments, the second wavelength is within a range of 500 nmto 850 nm. This can be realized by an embodiment comprising a secondlight source configured for providing light within this range. It canalso be realized by an embodiment in which the first light source isalso capable of emitting light at said second wavelength.

In some embodiments, the 3D scanner system comprises a dichroic mirrorconfigured for having a larger reflection coefficient at said secondwavelength than at wavelengths corresponding to the first wavelength andthe fluorescence, wherein the dichroic mirror is arranged such that itguides light from the second light source towards surfaces arrangedwithin the field of view and allows fluorescence received from the fieldof view to pass towards the image sensor.

In some embodiments, the dichroic mirror is arranged in the handheldpart of the 3D scanner system.

In some embodiments, the field of view for the recording of the 3Dsurface topography of the teeth and the field of view for recording offluorescence, respectively, are substantially identical.

In some embodiments, the field of view for the recording of imagescomprising probe light reflected and the field of view for recording offluorescence, respectively, are substantially identical. This allows forsimple and straightforward mapping of the fluorescence representationonto the digital 3D representation of the teeth created from the imagescomprising the reflected probe light.

In some embodiments, the 3D scanner system is configured to provide thata longer integration time is used when recording fluorescence comparedto the integration time used for recording the reflected light from thesurfaces of the intraoral cavity.

In some embodiments, the illumination unit, the image sensor and atleast one unit of the data processing means are integrated parts of ahandheld part of the 3D scanner system, such as handheld 3D scannerdevice. In embodiments comprising a first and a second light source,both light sources may be integrated parts of the handheld part of the3D scanner system.

In some embodiments, the 3D scanner system comprises imaging optics fortransmitting light received from one or more surfaces in the intraoralcavity to the image sensor when the 3D scanner is arranged in relationto the intraoral cavity.

In the context of the present invention, the phrase “3D scanner isarranged in relation to the intraoral cavity” describes a situationwhere the 3D scanning system is arranged such that it can illuminate atleast one surface of the intraoral cavity and/or arranged such thatlight from the intraoral cavity can be received and recorded by theimage sensor.

In embodiments, where the 3D scanner system comprises a handheld 3Dintraoral scanner configured for engaging the intraoral cavity, thephrase describes a situation where the handheld 3D intraoral scanner isarranged such that it can receive light from the intraoral surfaces.

In some embodiments, the imaging optics is also configured fortransmitting light from the illumination unit towards the surface of theintraoral cavity.

In embodiments, wherein the image sensor and the illumination unit arearranged in a handheld part of the 3D scanner system, the imaging opticsmay be an integrated part of the handheld part.

One way to realize a filtering means is to exploit that many opticalmaterials have lower transmissivity for some wavelengths or an inherentsensitivity dependence on wavelength of the image sensor. Both effectsare particularly noticeable when the light source emits deep blue or UVlight.

In some embodiments, the filtering means are defined by the spectralproperties of the optical elements of the imaging optics, such that theimaging optics provides the filtering function.

In some embodiments, the 3D scanner system comprises a control unitconfigured for controlling said illumination unit.

In some embodiments, the control unit is configured for controlling atwhich wavelength the first light source provides light at a given time.

In some embodiments, the control unit is configured for controlling thefirst light source such that the first light source alternatingly emitslight at the first wavelength and at the second wavelength.

It can be advantageous to use a significantly higher intensity of theprobe light for the excitation of the fluorescent tooth material thanwhen recording the images for the 3D surface topography. Normally theintensity of the emitted fluorescence is much weaker than the intensityof light reflected from the tooth surface. By illuminating the toothalternatingly with the light used for recording the 3D surfacetopography and the light used for exciting the fluorescence materials,the latter can be made more intense without saturating the image sensorby light reflected from the tooth surface.

In some embodiments, the control unit is configured for activating saidfirst and second light sources in such a manner that the illuminationunit sequentially emits light at said first and second wavelengths.

In some embodiments, the control unit is configured for controllingwhich of the first and the second light sources provide light at a giventime. The control unit may e.g., be configured for sequentially turningon/off the first and second light sources in such a manner that only oneof these light sources provides light to the field of view at any time.

In some embodiments, the control unit is configured for controllingoptical components of the 3D scanner system such that light at the firstand second wavelengths alternatingly is blocked, directed towards thefield of view of the 3D scanner system, or selected to pass toilluminate a surface of an intraoral cavity.

The data processing means may consist of a single processor unit or oftwo or more sub-units, such that the function of the data processingmeans are divided by these sub-units.

In some embodiments, the data processing means is a single dataprocessing unit configured for computing said sub-scans, for assigningsaid classification score and for said stitching.

In some embodiments, the data processing means comprises a number ofsub-units, where one sub-unit is a data processing unit configured forcomputing said sub-scans, and another sub-unit is a data processing unitconfigured for assigning said classification score and for saidstitching.

Such a single data processing unit or such a sub-unit may comprise astorage medium on which the appropriate algorithms are stored and a CPUconfigured for executing these algorithms.

In some embodiments, one sub-unit is arranged in a handheld part of the3D scanner system and one or more sub-units are arranged in a remotepart of the 3D scanner system, such as in a personal computer or a cartcomprising a screen for visualizing the recorded 3D surface topography.

In some embodiments, the data processing means is capable of applyingcomputer implemented algorithms configured for performing the computingof a series of sub-scans, the assigning of a classification score andthe stitching of sub-scans. The data processing means may comprise oneor more microprocessors capable of implementing such algorithms.

The data processing means may be capable of applying computerimplemented algorithms configured for computing a series of sub-scans.

The data processing means may be capable of applying computerimplemented algorithms configured for assigning classification scores.

The data processing means may be capable of applying computerimplemented algorithms configured for stitching the sub-scans.

In some embodiments, the data processing means are configured forcomputing said sub-scans for the intraoral cavity surface from thedetected light with said first wavelength. A series of sub-scans forsurfaces of the intraoral cavity can then be computed based on light atthe first wavelength reflected from the surfaces and detected by theimage sensor or by the further image sensor.

In some embodiments, the data processing means are configured forcomputing said sub-scans for the intraoral cavity surface from thedetected light with said second wavelength. A series of sub-scans forsurfaces of the intraoral cavity can then be computed based on light atthe second wavelength detected by the image sensor or by the furtherimage sensor.

In some embodiments, the data processing means comprises anon-transitory computer readable medium having one or more computerinstructions stored thereon, where said computer instructions comprisesinstructions for carrying out said algorithms.

In some embodiments, the 3D scanner system comprises means for filteringlight reflected by surfaces in the intraoral cavity from thefluorescence emitted by the hard dental tissue.

The filtering means may provide a filtering of light at the firstwavelength from the fluorescence emitted from the hard dental tissuewhen illuminated by light at the first wavelength.

The filtering means may provide a filtering of light at the secondwavelength from the fluorescence emitted from the hard dental tissuewhen illuminated by light at the first wavelength.

Such a filtering may be advantageous in cases where the fluorescenceemitted from the teeth is small compared to the intensity of the probelight. Filtering may then prevent saturation of the image sensor whichotherwise may occur before a sufficiently strong fluorescence signal isrecorded by the image sensor.

In some embodiments, the means for filtering comprises an optical filterwhich suppresses light at the first wavelength and/or light at thesecond wavelength more than it suppresses fluorescence emitted from thehard dental tissue when this is illuminated by light at said firstwavelength. Such a filtering may be advantageous in cases where thefluorescence emitted from the teeth is small compared to the intensityof the probe light. Filtering may then prevent saturation of the imagesensor which otherwise may occur before a sufficiently strongfluorescence signal is recorded by the image sensor.

In some embodiments, the filtering means provides a suppression of lightat the first wavelength by more than about 3 dB, such as by more thanabout 10 dB, such as by more than about 20 dB, such as by more thanabout 30 dB.

Due to scattering and/or transmission loss in optical filters there mayalso be a slight suppression of the fluorescence in the optical filter.The optical filter may be configured to provide a filtering function inwhich the ratio between the suppression of light at said first or secondwavelength and the suppression of the fluorescence is at least 5, suchas at least 10, such as at least 50, such as at least 50, such as atleast 100, such as at least 1000 or more.

In some embodiments the filtering means are implemented in the dataprocessing means.

In some embodiments, the filtering means are configured for digitallydecomposing the intensity of the signal detected by the image sensorinto one component relating to the fluorescence and into one or morecomponents relating to specular reflection, to diffuse reflection, andto stray light.

In some embodiments, the component relating to the specular reflectionis used for recording the 3D surface topography or for creating the 3Ddigital representation of the set of teeth.

In some embodiments, the classification score for a given portion of theintraoral cavity is determined at least from the fluorescence recordedfrom this portion.

In general, it may be advantageous to use sub-scans covering large areasand without restrictive filtering out of subsets of data within asub-scan, because the smaller surface area covered in sub-scans, thepoorer the stitching. This is particularly true when the surface haslittle 3D structure.

When fluorescence is excited with light of wavelengths at which the 3Dscanner system's image sensor is sensitive, for example near 400 nm, andno or non-perfect wavelength-discriminating optical filtering isapplied, the image sensor will effectively record a sum of at least someemission and at least some reflection. A relatively stronger signal willthus be obtained from hard dental tissue, but some signal also from softdental tissue.

In some embodiments, the representation of the emitted fluorescence iscreated by analyzing recorded images to identify sections of theseimages which correspond to fluorescence emitted from the teeth. This canbe realized by selectively reading pixels of the image sensor whichcorresponds to the fluorescence emitted from the fluorescent teethmaterial when this is illuminated by probe light at said firstwavelength.

In some embodiments, the representation of the fluorescence is a 2Drepresentation and said mapping comprises folding the 2D fluorescencerepresentation onto the digital 3D representation of the teeth.

Mapping the representation of the emitted fluorescence onto thecorresponding portion of the digital 3D representation of the teeth maybe defined as the adjustment of the fluorescence representation inrelation with the digital 3D representation of the teeth, such thatstructures of the digital representations are coinciding. Thus, commonor alike structures of the 3D digital representation comprisinggeometrical data of the teeth and the digital fluorescencerepresentation of the teeth are aligned.

Mapping to combine the digital representations may improve thevisualization of a cariogenic region. In some embodiments, this is doneby enhancing the visibility of the fluorescence representation bychanging its color or brightness such that the fluorescencerepresentation stands out more clearly in the visualized combineddigital 3D representation.

In the context of the present invention, the phrase “visualizing thecombined 3D representation” may refer to a visualization of all dataprovided by the combined 3D representation or to a visualization of apart of the data provided by the combined 3D representation. Thevisualized combined 3D representation may hence provide a visualizationof the extracted information rather than all the data which can beprovided from the 2D digital representation.

For a known geometry of the optical system of the 3D scanner system,such as the imaging optics and the illumination unit, and assuming norelative movement of the 3D scanner system and the intraoral cavityduring the acquisition of images from which the sub-scan is computed andthe fluorescence recording, a 2D image of fluorescence, which in essenceis a texture, can be mapped/folded onto the digital 3D representation ofthe surface topography.

The mapping of 2D image data of fluorescence to the 3D surface in asub-scan is particularly simple if both are obtained from the sameviewpoint and angle. In other words, it is beneficial for the 3D “depthimage” and 2D fluorescence image to match by design. One way toimplement such a design is to employ the same image sensor and imagingoptics for recording the images on which the 3D reconstruction is based,and the images of fluorescence.

As fluorescence emission between sub-scans can differ, for example dueto different distances to the teeth or due to different illuminationangles, the images of fluorescence may need to be intensity-adjusted forthe combined texture representing fluorescence on the entire 3D surfaceafter stitching. For example, texture weaving can be employed to smoothintensity differences between different sub-scans (Callieri et al 2002).

In practice, the assumption of no relative movement of 3D scanner andintraoral cavity during the 3D surface and fluorescence recordings willgenerally not hold perfectly. In embodiments of this invention thatswitch been fluorescence and 3D surface recordings, there may beadditional relative movement between those two phases.

In some embodiments, the representation of the fluorescence is a 3Drepresentation and said mapping comprises registering the 3Dfluorescence representation onto the digital 3D representation of theteeth.

The advantage of this is that in the combined digital 3D representation,the representation of the emitted fluorescence is arranged according toits true 3D position on the digital 3D representation of the teethproviding. A visualization of the combined digital 3D representation ishence accurate and allows, e.g., a dentist to precisely identify whichregions of the teeth are cariogenic.

In some embodiments, the data processing means are capable of mappingthe recorded fluorescence onto the digital 3D representation of theintraoral 3D surface topography, such as by mapping a digital 3Drepresentation of the fluorescence onto the digital 3D representation ofthe intraoral 3D surface topography.

The data processing means may comprise a storage medium on whichalgorithms for mapping the recorded fluorescence onto the digital 3Drepresentation of the intraoral 3D surface topography are stored and aCPU configured for executing these algorithms.

In some embodiments, the 3D scanner system is capable of visualizing themapped fluorescence on the digital 3D representation of the 3D surfacetopography. The 3D scanner system may comprise a visual display unit forvisualizing and computer code for manipulating the graphicalpresentation on the visual display unit.

In some embodiments, the data processing means are configured fordetecting differences in natural fluorescence of dentin and enamel. Thismay be detected using optical filters designed to distinguish betweenthe fluorescence of the dentin and enamel, by recording the spectraldistribution of the fluorescence or by digitally distinguishing betweenthe between the fluorescence of the dentin and the fluorescence of theenamel.

In some embodiments, the 3D scanner system is capable of visualizing thedifferences in dentin and enamel on the digital 3D representation of theintraoral 3D surface topography. The 3D scanner system may be capable ofproviding a visual presentation of the digital 3D representation inwhich the dental and enamel can be distinguished by using e.g.,different colors, textures, or opacities in the presentation or byallowing separate visualizations of the dentin and enamel to becontrolled independently, e.g., by varying the transparency of the twoindependently.

In some embodiments, the data processing means are configured fordetecting differences in fluorescence emitted from dental tissue, suchas hard or soft dental tissue, and that emitted from dental equipment,such as a retraction cord.

In some embodiments, the 3D scanner system is capable of visualizing thedifferences in dental tissue and dental equipment on the digital 3Drepresentation of the intraoral 3D surface topography. The 3D scannersystem may be capable of providing a visual presentation of the digital3D representation in which dental tissue and the dental equipment, canbe distinguished by e.g. using different colors, textures, or opacitiesin the presentation or by allowing separate visualizations of the dentaltissue and the dental equipment to be controlled independently, e.g. byvarying the transparency of the two independently.

In some embodiments, the data processing means are configured forextracting information from the recorded fluorescence and for combiningthe extracted information with the digital 3D representation of theintraoral 3D surface topography.

In some embodiments, the 3D scanner system is capable of visualizingsuch as combination of the information extracted from the recordedfluorescence and the digital 3D representation of the intraoral 3Dsurface topography.

Fluorescence can also be exploited for diagnosis of some dentaldiseases.

Enamel demineralization and thus early caries can be detected byquantitative light-induced fluorescence (QLF), which uses light withwavelengths around 405 nm to excite yellow fluorescence at wavelengthsabove 520 nm (Angmar-Måansson and ten Bosch 2001). QLF has also beenused to monitor tooth whitening (Amaechi and Higham 2001). Also,pathogenic microflora can display fluorescence and be thus detected(Sinyaeva et al 2004).

Some embodiments of the 3D scanner system of this invention are capableof combining the benefit of more accurate stitching with that of adiagnostic function. It is particularly advantageous for the dentistthat any diagnosed cariogenic region can be mapped onto the 3Drepresentation of the teeth and visualized as such.

In some embodiments, the data processing means are configured foridentifying cariogenic regions in which caries is present in more orless developed stages based on fluorescence detected from these areas.

In some embodiments, the 3D scanner system is configured for mapping acariogenic region of a tooth onto the portion of the digital 3Drepresentation of the 3D surface topography corresponding to said tooth.

The data processing means may be configured for providing arepresentation of the cariogenic region and mapping this representationonto the digital 3D representation of the 3D surface topography. Therepresentation may involve a coloring of the cariogenic region such thatthe cariogenic region is clearly visible in a visualization of thedigital 3D representation of the 3D surface topography with the mappedcariogenic region.

If teeth are illuminated with violet light in the spectrum of around 405nm, it causes dentin to emit fluorescence. Cariogenic bacteriaStreptococcus mutans produces special metabolites called porphyrins.These porphyrins fluoresce at red wavelengths, such as light in thewavelength range of 620-740 nm, when exposed to a 405-nm light, whilehealthy hard dental tissue fluorescence at green wavelengths, such aslight in the wavelength range of 520-570 nm.

In some embodiments, the first wavelength is within the range of 375 nmto 435 nm, such as in the range of 385 nm to 425 nm, such as in therange of 395 nm to 415 nm, such as in the range of 400 nm to 410 nm.

In some embodiments the 3D scanner system is configured for decidingwhether the fluorescence received from an illuminated portion of a toothhas a maximum intensity around 455 nm or in the range of 600 nm to 700nm. This can be realized by using a color image sensor comprising acolor filter array, such as the RGB filter array of a Bayer filter, andconfiguring the data processing means for comparing the readings in arecorded image such that the intensity of the blue pixels is compared tothe intensity of the red pixels.

In general, a crude measure of the spectral distribution of the emittedfluorescence can be realized by using a color image sensor comprising acolor filter array, such as the RGB filter array of a Bayer filter. Thepixels of the recorded image each belong to one of the colors of thefilter. The data processing means are then configured for comparing thereadings in the different pixels in a recorded image and from thatdetermine the ratio between e.g., the blue, green and red components ofthe emitted fluorescence.

When sound teeth are illuminated by light with a wavelength of 405 nmthe teeth emits fluorescence with a broad emission at 500 nm that istypical of natural enamel, whereas in caries teeth additional peaks areseen at 635 and 680 nm due to emission from porphyrin compounds in oralbacteria.

In some embodiments, the 3D scanner system is configured for decidingwhether the fluorescence received from an illuminated portion of a toothhas peaks in the range of 600 nm to 700 nm.

In some embodiments, the 3D scanner system is configured for decidingwhether the fluorescence received from an illuminated portion of a toothhas a maximum intensity around 455 nm or around 500 nm.

The deciding may be realized by optical components arranged to separatelight at the wavelengths.

The deciding may be realized by using a color image sensor with a Bayercolor filter array as the image sensor of the 3D scanner system andreading the ratio between the signals from the blue and green pixels ofthe image. In such a design, the green to blue ratio is significantlylarger for the 500 nm fluorescence than at 455 nm.

In some embodiments, the data processing means are capable of detectinga local decrease in the natural fluorescence of a tooth caused byscattering due to a caries lesion.

In some embodiments, a data processing means are capable of implementinga data analysis in which the spectral properties of the recorded imagesare taken into account.

A particular problem with stitching of intraoral sub-scans is softtissue in the oral cavity that moves between sub-scans and even within asub-scan. Overlapping regions in multiple sub-scans may therefore not beidentified correctly, deteriorating the quality of the stitchingalgorithm's result. In contrast, the parts of the sub-scans thatrepresent rigid objects such as teeth or prostheses, but also rugae inthe anterior palate, potentially allow better stitching.

Only hard dental tissue emits fluorescence when illuminated by a lightsource (Hartles 1953). The present invention utilizes this fact todifferentiate between hard and soft dental tissue in an intraoralcavity, such that the soft and hard dental tissues may be assigneddifferent weights in the stitching of sub-scans to provide a digital 3Drepresentation of the intraoral cavity. The differentiation of the hardand soft tissue can be such that the hard dental tissue is assigned ahigher weight that the soft dental tissue, such that potential errors inthe stitching due to e.g., movement or deformation of the soft tissueare mitigated.

The 3D scanner of the present invention is hence configured to measurethe natural fluorescence of hard dental tissue in addition to the 3Dtopographic characteristics of one or more surfaces of the intraoralcavity, and to differentiate between the soft and hard dental tissue inthe stitching of sub-scans based on this fluorescence.

Disclosed is hence a 3D scanner system for recording a 3D surfacetopography of a patient's intraoral cavity based on a series ofsub-scans, the intraoral cavity comprising soft dental tissue and harddental tissue, said 3D scanner system comprising:

-   -   an illumination unit configured for providing light at a first        wavelength, where light at said first wavelength can excite        fluorescent material of the hard dental tissue;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength; and    -   data processing means for:        -   i. computing sub-scans for the intraoral cavity surface,            each sub-scan representing a depth map of a region of said            intraoral cavity surface topography as seen from a given            position and orientation relative to said surface;        -   ii. assigning classification scores to portions of said            sub-scans relating to the hard dental tissue and to the soft            dental tissue, where said classification score            differentiates between the hard dental tissue and the soft            dental tissue, and where said classification score at least            partly is based on the recorded fluorescence; and        -   iii. stitching said sub-scans to create a digital 3D            representation of the intraoral 3D surface topography, where            the hard and soft dental tissues are weighted differently in            the stitching based on said classification scores.

Disclosed is a method for recording a 3D surface topography of apatient's intraoral cavity based on a series of sub-scans, the intraoralcavity comprising soft dental tissue and hard dental tissue, said methodcomprising:

-   -   obtaining a 3D scanner system according to any of the        embodiments;    -   scanning at least a part of the intraoral cavity using said 3D        scanner system and computing sub-scans relating to a number of        scanned regions of the intraoral cavity, each sub-scan        representing a depth map of a region of said intraoral cavity        surface topography as seen from a given position and orientation        relative to said surface;    -   assigning classification scores to portions of said sub-scans        relating to the hard dental tissue and to the soft dental        tissue, where said classification score differentiates between        the hard dental tissue and the soft dental tissue, and where        said classification score at least partly is based on        fluorescence recorded using said 3D scanner system;    -   stitching said sub-scans to create a digital 3D representation        of the intraoral 3D surface topography, where the hard and soft        dental tissues are weighted differently in the stitching based        on said classification scores.

Fluorescence of dentin and enamel has been observed to differ instrength at least for some excitation or observation wavelengths(Hartles 1953). By the same principle as the differentiation betweenhard and soft dental tissue, this phenomenon can be exploited todifferentiate the two materials. In particular, it can be exploited todetect a preparation line, which is particularly important to know whendental restorations are to be designed and manufactured.

The dentist often prepares a tooth below the gingival. This results inthe soft tissue wrapping around the sub-gingival preparation line andhinders scanning. To remedy this and allow for a clear view of thepreparation line the dentist can surround the prepared tooth byretraction cord. Such retraction cord can be made to fluoresce much morebrightly than hard tissue in the oral cavity by addition offluorophores. Such bright fluorescence can be exploited to detectpreparation lines, which is particularly important to know when dentalrestorations are to be designed and manufactured.

The soft dental tissue of the intraoral cavity may comprise gingiva,buccal tissue, tongue, or the tissue of the anterior palette.

The hard dental tissue of the intraoral cavity may comprise naturalteeth, the dentin or the enamel of a tooth, or a dental restoration.

While the 3D surface recording function of the 3D scanner system isbased on reflection from the surface which records both hard and softtissues, only the hard dental tissues emits fluorescence (Hartles 1953).Some dental restorations have also been observed to emit fluorescencewhen illuminated. This is advantageous because they too represent rigidstructures and thus valuable input for the stitching operation. In thesense of this invention, fluorescing dental restorations may thus beconsidered equivalent with dental hard tissue.

In some embodiments, the data processing means are configured to providethat the differentiation between hard and soft dental tissue and/or theassignment of classification scores to the hard and soft dental tissueis also based on the 3D topographic characteristics of the surface.

In some embodiments, the data processing means applies computerimplemented algorithms configured for stitching said sub-scans, wheresaid algorithms are configured for taking into account both informationderived from light reflected from the surface of the illuminated regionsof the surface of the intraoral cavity and information derived from thefluorescence emitted from the excited fluorescent materials in the harddental tissue in these portions.

Some soft tissue in the oral cavity, particularly at the anteriorpalate, is in fact rather rigid, and even more advantageously for thepurpose of stitching, it has a clear 3D structure, the rugae. It canthus be advantageous to not only differentiate tissue types byfluorescence (or, as in U.S. Pat. No. 7,698,068, by color), but also bystructure. Rugae can for example be detected due to their approximatelyknown 3D surface structure. For some orthodontic appliances, knowledgeof the 3D geometry of the palate is important, so an intraoral 3Dscanner should preferably be able to record it.

In some embodiments, the classification score relates to a probabilityof belonging to a class of soft dental tissue or a class of hard dentaltissue.

In some embodiments, the classification score further divides softdental tissue into soft tissue sub-classes, such as gingiva, buccaltissue, tongue, rugae in the hard anterior palate.

An advantage of further dividing the soft tissue is that the position ofsome types of soft tissue relative to the other parts of intraoralcavity is relatively fixed. The anterior palette e.g., cannot move asmuch as the tongue.

In some embodiments, the classification score further divides harddental tissue into hard tissue sub-classes, such as natural teeth,dental restorations, the dentin, or the enamel of a tooth.

The data processing means may then be configured for assigning aprobability for a portion of the sub-scans of belonging to a given softtissue sub-class.

The data processing unit may then be configured for assigning aprobability for a portion of the sub-scan of belonging to a given hardtissue sub-class.

In some embodiments, the data processing means are configured forassigning a classification score to equipment used in a dentalprocedure, such as a retraction cord placed in the intraoral cavity bye.g., a dentist during a dental procedure.

In some embodiments, the classification score comprises a numericalvalue.

The classification score and the weighting of sub-scans based on thisclassification score may be such that a relatively higher numericalvalue indicates that the corresponding portion is weighted higher in thestitching.

The classification score and the weighting of sub-scans based on thisclassification score may be such that a relatively lower numerical valueindicates that the corresponding portion is weighted higher in thestitching.

In some embodiments, the relative value of the classification scores fortwo portions of a sub-scan relating to different classes or sub-classesof dental tissue determines the relative weight these two portions havein the stitching.

In some embodiments, the classification scores for hard and soft dentaltissue are such that hard dental tissue is weighted higher than softdental tissue in the stitching.

In some embodiments, the classification scores for rugae of the anteriorpalette and other kinds of soft dental tissue, such as the buccal tissueand the tongue, are such that said rugae is weighted higher than theother kinds of soft dental tissue in the stitching.

This provides the advantage that the stitching of sub-scans can beimproved compared to when all soft tissue is weighted equally.

In some embodiments, the weighting is such that hard dental tissue has aweight which is 5 times higher than the soft dental tissue, such as 10times higher, such as 15 times higher, such as 25 times higher, such as50 times higher, such as 75 times higher, such as 100 times higher oreven more.

In some embodiments, utilizing an iterative closest point procedure, thelocal distance between corresponding portions of two point clouds ismultiplied with the classification score such that a distance isweighted highly for a high classification score and a distance has a lowweight for a low classification score.

In some embodiments, the relative weighting of the different regions isgiven by a linear relationship:

w _(n,m) =k ₁ c _(n,m) +k ₂

where n is a label identifying a scanned surface element, m is thesub-scan label, w_(n,m) is the weight used for surface element n in thestitching of sub-scan m to create the 3D representation of the intraoral3D surface, c_(n,m) is the fluorescence dependent signal recorded forsurface element n in sub-scan m, and k₁ and k₂ are constants determinedbefore the scanning.

In some embodiments, the relative weighting of the different regions isgiven by a second order polynomial where a second order term is added:

w _(n,m) =k ₁(c _(n,m))² +k ₂ c _(n,m) +k ₃

where the constants k₁, k₂, and k₃ are determined before the scanning.

In some embodiments, the relative weighting of the different regions isgiven by a more general expression:

w _(n,m) =f(n,c _(m))

where c_(m) is the collection of all fluorescence dependent signalsrecorded for sub-scan m. This more general expression includes schemeswhere edges or gradients in the fluorescence-dependent signal are usedin assigning soft/hard tissue classification in surface element n.

The relative weighting may be described by a step function where thedifferent classes of tissue a taken into account if their classificationscore is above a certain threshold value.

Because of all the above described uncertainties with differentiatingsoft and hard tissue, and because of the benefits of recording at leastpart of the soft tissue, it is not advisable to completely ignoresupposed, but in actuality misclassified, soft tissue in the stitching.U.S. Pat. No. 7,698,068 according to its claim 1, in contrast, teachesto stitch sub-scans based on “only a first portion” thereof, i.e., toperform a complete and fully discriminating segmentation of the 3Dsurface data by color before stitching. This invention, in contrast,holds that it is advantageous to assign the supposed soft tissues asmaller, but non-zero weight in the stitching algorithm. Many suchstandard algorithms, e.g., ICP, are based on sum of some norm ofdistance deviations between regions of sub-scans, and can simply beextended to weighted sums, for example a weighted sum of squareddistances.

In some embodiments, the data processing means are configured for takinginto account the risk of assigning a false classification score of aportion of the intraoral cavity.

It can also be advantageous to detect hard tissue not only fromfluorescence, but at least partly also based on 3D surface structure.For example, canine, premolar, and molar teeth have an at leastapproximately known occlusal surface with a number of cusps.

In some embodiments, the classification score for a given portion of theintraoral cavity is determined at least partly from an identification ofthe portion based on the surface topography is this portion. Theidentified portion of the intraoral cavity may relate to a canine, apremolar, or a molar tooth. An example of a suitable algorithm formaking such identification is described in Kronfeld et al 2010. Therugae of the anterior palette with its characteristic surface modulationcan also be used for this purpose.

For some applications of a 3D scanner system, it is advantageous toprovide a higher precision and/or spatial resolution for a region ofparticular interest. The region of particular interest can be marked inthe intraoral cavity using dental equipment, such as a retraction cordarranged to at least partially surround the region. Based on thefluorescence emitted from it, the dental equipment can be identified ina sub-scan or in the stitched digital 3D representation of the intraoral3D surface topography such that its location relative to the dentaltissue can be determined. When the dental equipment marks a boundarybetween the region of particular interest and the remaining regions ofthe intraoral cavity knowledge of its location can be used forautomatically identifying the region of particular interest in thecreated digital 3D representation.

Disclosed is hence a 3D scanner system for recording a 3D surfacetopography of a patient's intraoral cavity based on a series ofsub-scans acquired with dental equipment arranged in the intraoralcavity, where the dental equipment comprises a fluorescent materialwhich emits fluorescence when illuminated by light at a firstwavelength, said 3D scanner system comprising:

-   -   an illumination unit configured for providing light at said        first wavelength;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength; and    -   data processing means for:        -   i. computing sub-scans for the intraoral cavity surface,            each sub-scan representing a depth map of a region of said            intraoral cavity surface topography as seen from a given            position and orientation relative to said surface;        -   ii. stitching said sub-scans to create a digital 3D            representation of the intraoral 3D surface topography; and        -   iii. identifying the dental equipment in a sub-scan or in            the stitched digital 3D representation of the intraoral 3D            surface topography and determining the position of the            dental equipment relative to the dental tissue based on            recorded fluorescence emitted from the dental equipment.

In some embodiments, the settings of the 3D scanning, such as the numberof images acquired for the computation of each sub-scan, can be adjustedduring a 3D scanning. With an appropriate change of the settingssub-scans with a higher precision and/or resolution can be obtained forselected regions, such as for a region of particular interest.

The region of particular interest may e.g., relate to a prepared toothfor which a dental restoration is to be designed based on the digital 3Drepresentation of the intraoral 3D surface topography.

In some embodiments, the data processing means are configured to providethat when the dental equipment is arranged such that it marks a boundarybetween a region of particular interest and the remaining regions of theintraoral cavity, the data processing means are capable of identifyingthe portion of the digital 3D representation corresponding to the regionof particular interest based on the fluorescence from the dentalequipment recorded by the image sensor.

In some embodiments, the data processing means are capable of deriving avirtual model of the dental equipment based on the fluorescence recordedfrom the dental equipment, and where the position of the boundary in thedigital 3D representation is determined based on this virtual model.

In some embodiments, deriving the virtual model of the dental equipmentcomprises matching the fluorescence recorded from the dental equipmentwith a template virtual model from a dental equipment library.

In some embodiments, the identification of the region of particularinterest also is based on an analysis of the recorded 3D surfacetopography.

In some embodiments, the 3D scanner system is capable of adjusting thesettings relating to the precision and/or spatial resolution at whichthe 3D scanner system acquires data from surface for computing thesub-scans, such that a higher precision and/or resolution can beprovided for the region of the digital 3D representation correspondingto the region of particular interest.

In some embodiments, the method is such that the classification scoredifferentiates between different sub-classes of hard dental tissue, suchas natural teeth, dental restorations, dentin/enamel and/or wherein saidclassification score further differentiates between differentsub-classes soft dental tissue, such as gingiva, buccal tissue, tongue,rugae in the hard anterior palate.

In some embodiments, the method is such that the assigned classificationscore relates to a probability for a portion of a surface in a givensub-scan to belong to a given soft dental tissue class, soft dentaltissue sub-class, hard dental tissue class, or hard dental tissuesub-class.

In some embodiments, the method is such that the assigned classificationscore is a numerical value indicating the weight of the portion in thestitching of the sub-scans.

In some embodiments, the method comprises determining a preparation linebased on differences in the fluorescence emitted from the dentin and theenamel of a prepared tooth.

In some embodiments, the 3D scanner system comprises a handheld part andwherein said handheld part is moved relative to said intraoral cavitybetween acquisitions of different sub-scans.

Disclosed is a 3D scanner system for detecting caries in teeth of apatient's intraoral cavity, said 3D scanner system comprising:

-   -   an illumination unit configured for providing light at a first        wavelength, where light at said first wavelength can excite        fluorescent material of the teeth;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength;    -   data processing means for:        -   i. creating a digital 3D representation of the patient's set            of teeth;        -   ii. analyzing the recorded fluorescence to identify            cariogenic regions of the teeth;        -   iii. creating a representation of identified cariogenic            regions; and        -   iv. mapping the representation of identified cariogenic            regions onto the corresponding portion of the digital 3D            representation of the teeth to provide a combined digital 3D            representation; and    -   a visual display unit on which the combined digital 3D        representation can be visualized.

Disclosed is a 3D scanner system for detecting caries in teeth of apatient's intraoral cavity based on a series of sub-scans, said 3Dscanner system comprising:

-   -   an illumination unit configured for providing light at a first        wavelength, where light at said first wavelength can excite        fluorescent material of the teeth;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength;    -   data processing means for:        -   i. computing sub-scans for the intraoral cavity surface,            each sub-scan representing a depth map of a region of said            intraoral cavity surface topography as seen from a given            position and orientation relative an intraoral cavity            surface;        -   ii. stitching said sub-scans to create a digital 3D            representation of the patient's set of teeth;        -   iii. analyzing the recorded fluorescence to identify            cariogenic regions of the teeth; and        -   iv. mapping cariogenic regions onto the corresponding            portion of the digital 3D representation of the teeth to            provide a combined digital 3D representation in which the            cariogenic regions are arranged according to their true            position on the teeth; and    -   a visual display unit on which the combined digital 3D        representation can be visualized.

3D modeling is the process of developing a mathematical, wireframerepresentation of any three-dimensional object, called a 3D model, viaspecialized software. Models may be created automatically, e.g., 3Dmodels may be created using multiple approaches: use of NURBS curves togenerate accurate and smooth surface patches, polygonal mesh modelingwhich is a manipulation of faceted geometry, or polygonal meshsubdivision, which is advanced tessellation of polygons, resulting insmooth surfaces similar to NURBS models.

The intra-oral scanner may be configured for utilizing focus scanning,where the digital 3D representation of the scanned teeth isreconstructed from in-focus images acquired at different focus depths.The focus scanning technique can be performed by generating a probelight and transmitting this probe light towards the set of teeth suchthat at least a part of the set of teeth is illuminated. Light returningfrom the set of teeth is transmitted towards a camera and imaged onto animage sensor in the camera by means of an optical system, where theimage sensor/camera comprises an array of sensor elements. The positionof the focus plane on/relative to the set of teeth is varied by means offocusing optics while images are obtained from/by means of said array ofsensor elements. Based on the images, the in-focus position(s) of eachof a plurality of the sensor elements or each of a plurality of groupsof the sensor elements may be determined for a sequence of focus planepositions.

The in-focus position can e.g., be calculated by determining the lightoscillation amplitude for each of a plurality of the sensor elements oreach of a plurality of groups of the sensor elements for a range offocus planes. From the in-focus positions, the digital 3D representationof the set of teeth can be derived.

Iterative Closest Point (ICP) is an algorithm employed to minimize thedifference between two clouds of points. ICP can be used to reconstruct2D or 3D surfaces from different scans or sub-scans. The algorithm isconceptually simple and is commonly used in real-time. It iterativelyrevises the transformation, i.e., translation and rotation, needed tominimize the distance between the points of two raw scans or sub-scans.The inputs are: points from two raw scans or sub-scans, initialestimation of the transformation, criteria for stopping the iteration.The output is: refined transformation. Essentially the algorithm stepsare:

-   -   1. Associate points by the nearest neighbor criteria.    -   2. Estimate transformation parameters using a mean square cost        function.    -   3. Transform the points using the estimated parameters.    -   4. Iterate, i.e., re-associate the points and so on.

The present invention relates to different aspects including the systemand method described above and in the following, and correspondingsystems and methods, each yielding one or more of the benefits andadvantages described in connection with the first mentioned aspect, andeach having one or more embodiments corresponding to the embodimentsdescribed in connection with the first mentioned aspect and/or disclosedin the appended claims.

Disclosed is a 3D scanner system for recording a 3D surface topographyof a patient's intraoral cavity based on a series of sub-scans, theintraoral cavity comprising soft dental tissue and hard dental tissue,said 3D scanner system comprising:

-   -   an illumination unit configured for providing light at a first        wavelength, where light at said first wavelength can excite        fluorescent material of the hard dental tissue;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength;    -   means for generating a series of sub-scans for the intraoral        cavity surface based on the light captured by the image sensor,        where each sub-scan represents a depth map as seen from a given        position and orientation relative to the intraoral cavity        surface; and    -   a data processing means for:        -   at least partly differentiating dental hard and soft tissue            based on fluorescence emitted from fluorescent material in            the hard dental tissue, and for        -   stitching said sub-scans to create a digital 3D            representation of the intraoral 3D surface topography, where            the hard and soft dental tissues are weighted differently in            the stitching.

In some embodiments, the different weighting in the stitching is basedon the result of the differentiating of hard and soft tissue.

According to an aspect of the invention is a 3D scanner system forrecording a 3D surface topography of a patient's intraoral cavity basedon a series of sub-scans, the intraoral cavity comprising soft dentaltissue and hard dental tissue, said 3D scanner system comprising:

-   -   an illumination unit configured for providing light at a first        wavelength, where light at said first wavelength can excite        fluorescent material of the hard dental tissue;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength; and    -   data processing means for:        -   i. computing sub-scans for the intraoral cavity surface,            each sub-scan representing a depth map of a region of said            intraoral cavity surface topography as seen from a given            position and orientation relative to said surface;        -   ii. assigning classification scores to portions of said            sub-scans relating to the hard dental tissue and to the soft            dental tissue, where said classification score            differentiates between the hard dental tissue and the soft            dental tissue, and where said classification score at least            partly is based on the recorded fluorescence; and        -   iii. stitching said sub-scans to create a digital 3D            representation of the intraoral 3D surface topography, where            the hard and soft dental tissues are weighted differently in            the stitching based on said classification scores.

According to an aspect of the invention is a method for recording a 3Dsurface topography of a patient's intraoral cavity based on a series ofsub-scans, the intraoral cavity comprising soft dental tissue and harddental tissue, said method comprising:

-   -   obtaining a 3D scanner system according to any of the        embodiments;    -   scanning at least a part of the intraoral cavity using said 3D        scanner system and computing sub-scans relating to a number of        scanned regions of the intraoral cavity, each sub-scan        representing a depth map of a region of said intraoral cavity        surface topography as seen from a given position and orientation        relative to said surface;    -   assigning classification scores to portions of said sub-scans        relating to the hard dental tissue and to the soft dental        tissue, where said classification score differentiates between        the hard dental tissue and the soft dental tissue, and where        said classification score at least partly is based on        fluorescence recorded using said 3D scanner system;    -   stitching said sub-scans to create a digital 3D representation        of the intraoral 3D surface topography, where the hard and soft        dental tissues are weighted differently in the stitching based        on said classification scores.

According to an aspect of the invention is a 3D scanner system fordetecting caries in teeth of a patient's intraoral cavity, said 3Dscanner system comprising:

-   -   an illumination unit configured for providing light at a first        wavelength, where light at said first wavelength can excite        fluorescent material of the teeth;    -   an image sensor configured for recording fluorescence emitted        from the fluorescent material when this is excited by light at        said first wavelength;    -   data processing means for:        -   i. creating a digital 3D representation of the patient's set            of teeth;        -   ii. analyzing the recorded fluorescence to identify            cariogenic regions of the teeth;        -   iii. creating a representation of identified cariogenic            regions; and        -   iv. mapping the representation of identified cariogenic            regions onto the corresponding portion of the digital 3D            representation of the teeth to provide a combined digital 3D            representation; and    -   a visual display unit on which the combined digital 3D        representation can be visualized.

Furthermore, the invention relates to a computer program productcomprising program code means for causing a data processing system toperform the method according to any of the embodiments, when saidprogram code means are executed on the data processing system, and acomputer program product, comprising a computer-readable medium havingstored there on the program code means.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional objects, features and advantages of thepresent invention, will be further elucidated by the followingillustrative and non-limiting detailed description of embodiments of thepresent invention, with reference to the appended drawings, wherein:

FIG. 1 shows an embodiment of the 3D scanner system according to thepresent invention.

FIG. 2 shows an embodiment of the 3D scanner system according to thepresent invention with the first light source is mounted near the frontof a tip of a handheld part of the 3D scanner system.

FIG. 3 shows an embodiment of this invention with a single light source.

FIG. 4 illustrates how hard and soft dental tissue can be differentiatedbased on a recorded fluorescence from the hard dental tissue.

FIGS. 5A and 5B show how the data processing means can analyze theintensity of the light recorded by the image sensor.

DETAILED DESCRIPTION

In the following description, reference is made to the accompanyingfigures, which show by way of illustration how the invention may bepracticed.

The figures below illustrate schematically how embodiments of a 3Dscanner according to this invention can be realized. The figures are notnecessarily dimensionally precise.

FIG. 1 shows an embodiment of the invention, namely a focus scanningintraoral 3D scanner comprising an illumination unit with a first lightsource 210 and a second light source 110, a pattern 130 (a line in atrue cross-sectional view, but shown here at an angle for clarity), animage sensor 180, a beam splitter 140, and focusing optics with amoveable lens 151. The 3D scanner has a tip or probe 170 with a mirror172 that folds the beam path towards the region of the intraoral cavitybeing scanned 300. The intraoral cavity comprises hard dental tissue 301and soft dental tissue 302. The second light source 110 emits light atleast at the second wavelength and may comprise collimation optics. Inthe figure, the short thin dashed lines illustrate light rays emittedfrom the second light source and imaged through the optical system ontothe object being scanned, returned through the optical system, and lightrays imaged onto the image sensor. The 3D surface topography of thepatient's intraoral cavity is recorded based on images acquired with theimage sensor when the object is illuminated with light from the secondlight source. The second light source 110 is thus intended for 3Dsurface recording, and the first light source 210 may be turned offduring 3D surface recording.

The 3D scanner can include other elements as well; however, they are notessential for this invention and are not illustrated in the figure. Adetailed description of a focus scanning device including otherpotentially beneficial elements and the associated calculations is givenin WO2010145669.

The first light source 210 of the illumination unit of the embodimentshown in FIG. 1 is configured for emitting light at the first wavelengthintended to excite fluorescence in the hard tissue parts of theintraoral cavity 300. A dichroic mirror 200 directs the light from thefirst light source 210 towards mirror 172. The dichroic mirror 200 istransmissive to the wavelengths generated by the second light source 110and fluorescence from the hard tissue 301, but reflective to thosegenerated by the first light source 210. Mirror 172 is reflective atwavelengths generated by the first and second light sources 110, 210,and fluorescence from the hard tissue 301. Light rays emitted by thefirst light source 210 are illustrated as lines with thick, long dashes.The light at the first wavelength excites fluorescence in the hardtissue parts 301. A portion of the emitted fluorescence follows thesubstantially same path as the light from the second light source 110after it is reflected from the dental cavity, such that this portion ofthe emitted fluorescence can be directed towards the image sensor 180 bythe beam splitter 140.

The first light source 210 can be a LED with an emission peak at 405 nm,and the second light source 110 can be an LED with an emission peakabove 520 nm, for example at 590 nm.

As indicated by the double-sided arrow in FIG. 1 , during a 3D scan thefocus of the optical system is swept from one end of the focus volume tothe other end by moving the focus lens 151 in the direction along themain optical axis. The focus sweep translates the focus in a directionsubstantially along the optical axis of the optical system. During thefocus sweep a stack of images is obtained with the image sensor 180.

As described in WO2010145669, a correlation measure A, within a block ofpixels representing one region of the checkerboard pattern shown in FIG.1 can be determined by means of the following formula:

$A = {{\sum\limits_{i = 1}^{n}{f_{i}I_{i}}} = {f \cdot I}}$

where n is the number of pixels within the block, f is the referencesignal vector obtained from knowledge of the pattern configuration aftera calibration, and I is the input signal vector, i.e., the intensitiesrecorded in the pixels. The block can be a square block of pixelscovering the image of at least one period of the checkerboard pattern,for example n=2×2 or n=4×4 or n=6×6. The 3D coordinates for each suchblock are then determined from the location of the maximum of A over theseries of images in a focus sweep. Note that with the above method, the3D coordinates of both hard tissue 301 and soft tissue 300 are found.For the details of the calculations including a method to find f, seeagain WO2010145669.

In the embodiment illustrated in FIG. 1 , the image sensor 180 can alsobe used for measuring fluorescence, i.e., the light emitted by thedental hard issue after excitation. In this mode, the second lightsource 110 is turned off, while the first light source 210 is turned on.In particular a focus scanner is characterized by a shallow depth offocus, and hence a single image will not be sharp over the range ofdepths typically encountered in a view of the intraoral cavity. One wayto obtain a sharp image over all locations of the focus planes during asweep is to generate a “fused image” that combines the sections that areoptimally in focus from all images taken during a sweep.

A detailed description of how this step may be performed is illustratedin FIG. 17 and the associated text of WO2010145669. The recording of animage of fluorescence can be based on an entire sweep of the focus lens,just like the acquisition of a 3D sub-scan. It may also be admissiblefor some applications to accept imperfect sharpness of the fluorescenceimage, and only take a few images of fluorescence during the sweep, forexample when the focus lens is at its extreme positions, and to “fuse”those as described in WO2010145669.

It may be advantageous to increase exposure time of the image sensorwhen fluorescence is recorded. This is so because the intensity of thefluorescence-emitted light can be smaller than that of the reflected3D-recording light, i.e., when the second light source 110 is on. If thespeed of the focus lens is the same as during 3D surface recording, alonger exposure time results in fewer images taken during a sweep, andhence the “fused” image is less sharp. Alternatively, the speed of thefocus lens can be reduced, which from optical reasoning should givesharper “fused” images, but in actuality comes at a risk of loss ofsharpness due to hand or patient movement during the relatively longersweep.

The intensity of the fluorescence image can be used as a relative weightin the stitching algorithm, expressing the level of certainty in theclassification as hard dental tissue. Note that the stitching imagespresent all pixels of the sensors, whereas the 3D coordinates arecomputed for a block of pixels according to equation (1). Thus, it canbe advisable to find an average intensity for the corresponding pixelblock in the fluorescence image and associate that with the 3Dcoordinate found for the pixel block.

FIG. 2 shows an embodiment of this invention where the first lightsource 210 is mounted near the front of the tip 170. The advantage ofthe embodiment in FIG. 1 is that no dichroic mirror is required. On theother hand, it is more challenging to mount the first light source 210in the typically limited space of the tip or probe 170. Electricalinsulation is also more difficult in a location so close to the patient.On the other hand, a side benefit of the arrangement in FIG. 2 is that ametal part of the tip/probe 170 can be used as the heat sink for an LEDfirst light source 210, potentially also heating optical elements in thetip (not shown in FIG. 2 ) by waste heat. Heating such optical elementscan prevent condensation that may otherwise occur when the tip/probe isentered into the patient's oral cavity.

If the first light source 210 emits wavelengths at which the imagesensor 180 is responsive, because there is no filtering by any dichroicmirror, it is advantageous to arrange an optical filter 281 in front ofthe image sensor 180 to block light from the first light source unlessthe data processing means are configured for distinguishing betweenlight from the first and the second light source. This optical filterallows the wavelengths of the second light source 110 for the 3D surfacerecording and the emitted fluorescence to pass, but not those excitingthe fluorescence. If the light at the first wavelength emitted by thefirst light source 210 is near or below 400 nm, standard opticalelements often act as effective filters, and many image sensors are onlypoorly sensitive to those wavelengths. In this situation, a dedicatedfilter 281 may not be needed at all.

Connected to the image sensor 180 is the data processing means 400comprising a storage medium on which the appropriate algorithms arestored and a CPU configured for executing these algorithms. The dataprocessing means 400 are configured for creating a digital 3Drepresentation of the 3D topography of the teeth based on recordedimages comprising probe light reflected from the teeth; for creating arepresentation of the fluorescence emitted from the fluorescent materialof the teeth based on recorded images comprising the emittedfluorescence, and for mapping the representation of the emittedfluorescence onto the corresponding portion of the digital 3Drepresentation of the teeth to provide a combined digital 3Drepresentation.

The 3D scanner system further comprise a visual display unit 500connected to the data processing means 400 on which visual display unitthe combined digital 3D representation is visualized.

The two light sources in the embodiment of FIG. 2 are turned on and offalternatingly in the same manner as described for the embodiment of FIG.1 .

FIG. 3 shows an embodiment of this invention with a single light sourceconfigured for both exciting fluorescence and for recording the 3Dsurface topography.

The illumination unit is here a single light source unit with only thefirst light source 310 arranged to illuminate a surface of an intraoralcavity. The first light source 310 emits light with a peak emittance at405 nm, such that the light from the first light source is suitable forboth exciting the fluorescent material in the hard dental tissue 301 andfor projecting the pattern 130 onto the region of the intraoral cavitybeing scanned 300 to record the 3D surface topography of this region.The mirror 172 is reflective both at the wavelength of the lightprovided by the first light source and at the wavelength of thefluorescence emitted from the hard dental tissue 301, such that lightreflected from the surfaces of the intraoral cavity and the fluorescenceis collected and guided towards the image sensor 180.

In the illustrated embodiment, the composition of physical elements isas taught in WO2010145669.

The data processing performed by the data processing means may bedifferent.

A least partial separation of the signal relating to the fluorescenceand the signal relating to the reflected light occurs in the dataprocessing means, as described in the following, and enhanced byappropriate optical design, as described further below.

FIG. 4 shows the advantage of recording fluorescence for the purpose ofdifferentiating hard and soft dental tissue. The figure shows threeimages taken by a 3D scanner system according to this invention, takenof similar scenes showing two teeth and at the bottom some gingival in ahuman intraoral cavity. For image (a), the scene was illuminated with ared LED with peak emission at 630 nm. For image (b), the scene wasilluminated with a deep blue LED with peak emission at 400 nm, and a 450nm long-pass optical filter rejecting radiation at wavelengths below 450nm was inserted before the image sensor. For image (c), illumination wasas in (b), but no optical filter was applied. As can be seen from (a),the difference in reflectance between hard and soft tissue for red lightis very small, and hence differentiation is unclear. In image (b)fluorescence from the illuminated region is recorded, and a scan be seenfrom (b), fluorescence alone yields strong differentiation allowing hardtissue to be distinguished from the soft tissue, but a weaker signal.Note also that as expected when only fluorescence is recorded, nospecular reflections are visible in (b), unlike in (a) and (c). Image(c) shows that the combination of reflectance of deep-blue light and thefluorescence emitted from fluorescent materials in the hard dentaltissue when excited by the blue light yields a good signal and rathergood discrimination. It is not perfect, however, due to some specularreflections from the gingival. Image (c) thus demonstrates thatstitching as taught by U.S. Pat. No. 7,698,068 is not optimal. Note thatthe images are not perfectly sharp because they were taken with thefocus lens in one position.

The images in FIG. 4 are also representative of texture images that canbe mapped on a digital 3D representation of the 3D surface topography.Note that while 3D coordinates are computed for a block of pixels, thetexture represents individual pixels.

WO2010145669 did not differentiate between various contributions to therecorded intensities I, but that additional analysis is fundamental todescribe and understand the single light source embodiment of theinvention where the soft and hard tissues are distinguished by the dataprocessing means. In particular, I can be written as

I=I _(sr) +I _(dr) +I _(f) +I _(s)  (2)

where the subscripts are sr for specular reflection, dr for diffusereflection including sub-surface reflection, f for fluorescence, and sfor stray light. In the following, without loss of generality we assumethat I_(s)=0 since the component of stray light is negligibly small orcan be compensated for in an appropriate optical design.

When the projection of the pattern 130 is in focus on a part of theintraoral cavity 300 being scanned, the recorded intensity from specularreflection from this in-focus region will display the projected pattern130 on the image sensor. As a result, is, will vary laterally on thescanned surface. It is advantageous for the 3D scanner to be able toscan the oral cavity with high resolution. Preferably, the lateralresolution is 100 μm or less. This implies the need for the features ofthe projected pattern to be correspondingly small. The diffusion lengthof both the light diffusively reflected from the hard tissue and thefluorescence light generated inside the hard tissue is generally longerthan 100 μm. Hence I_(dr) and I_(f) will display little or no lateralvariation.

FIG. 5A illustrates a part of a recorded image corresponding to anin-focus surface for a single lateral coordinate x, i.e., a coordinatein a plane perpendicular to the line of sight to the surface from the 3Dscanner. The relative magnitude of the different components shown in thefigure is only for illustrative purposes and may be different in aparticular embodiment of the invention. As WO2010145669 teaches, therelevant signal for recording 3D geometry of the intraoral cavity is theintensity due to the specular reflection, I_(sr).

WO2010145669 describes ways of using polarizing elements to reduce asignal from the depolarized, diffuse reflection. Light emitted byfluorescence has in similarity to the diffusively reflected light noparticular polarization state and will be affected by any polarizingelements in the same manner as diffuse reflection.

The decomposition of intensity expressed in equation (2) can be insertedinto equation (1) to describe the decomposition of the correlationmeasure A. WO2010145669 teaches that it is advantageous that thereference signal f is so normalized that:

${\sum\limits_{i = 1}^{n}f_{i}} = 0$

It follows that the contributions to the recorded DC signals from I_(dr)and I_(f) do not contribute or at least not significantly to thecorrelation measure A.

FIG. 5B shows an example for a focus sweep of a given pixel block, i.e.,with A as a function of focus lens position z. At location 1802, theprojection of the pattern is in focus on the surface, and hence thecorrelation measure is at a maximum.

The 3D scanner observes A, the sum of all contributions, but does not,in itself, provide a strong differentiation of hard from soft dentaltissue since the specular reflection is not very different between hardand soft tissue surface. The minimum value of the recorded signal I onthe sensor within a group of pixels will correspond to the sum of I_(df)and I_(f). It is seen in FIG. 4 (c) that the sum of I_(df) and I_(f) ishigher for hard tissue than for soft tissue and this provides adifferentiation of hard and soft tissue.

A calibration step can help quantify the sum I_(df)+I_(f). For example,the user of the 3D scanner can be guided to first scan a tooth and thenan area of the gingival, such that (I_(df)+I_(f)) can be computed as thedifference in minimum values of I in an in-focus region (see FIG. 5A).It may be further advantageous to repeat the calibration at varyingangles of incidence in case I is found to depend thereon for aparticular case. The angle of incidence need not be measured by anyadditional instrument; the 3D scanner measures the 3D surface in anycase and at least a local gradient approximation can be computed.

The above analysis, as illustrated in FIGS. 5A and 5B, shows is thenovelty of some embodiments of this invention over WO2010145669. Whilethe latter only teaches how to find the location of the extremum of A,this invention requires an analysis of the background intensity on thesensor with little or no lateral variation over a pixel group. Foradditional information on finding the in-focus location by analysis ofthe variation of A, see particularly the section “Spatial Correlation”and FIG. 18 and the accompanying text of WO2010145669.

One way to enhance the differentiation between hard and soft tissue isto choose optical elements that transmits the fluorescence relativelybetter. Assuming for the sake of simplicity a first light sourceemitting light with a single wavelength 405 nm and fluorescence emittedat 520 nm, using the wavelength as subscript, and looking only at theintensity recorded in a single pixel, we can write:

I _(sr) ∝I _(0,405) t ₄₀₅ rt′ ₄₀₅

I _(f) ∝I _(0,405) t ₄₀₅ ηt′ ₅₂₀

where I₀ is the intensity emitted from the light source, t is thetransmissivity of the optical system along the path from light source tothe intraoral cavity, r is reflectivity, η is emissivity due tofluorescence, and t′ is the transmissivity of the optical system alongthe path from the intraoral cavity to the image sensor. Because η istypically considerably smaller than r, it may be advantageous to providethat the design of the optical system is such that t′₅₂₀ is larger thant′₄₀₅, such that the contribution from fluorescence in the overallsignal I is significant.

Another way to enhance the differentiation between hard and soft tissueis to use a blue light source, because diffuse reflection fromessentially white teeth shows little dependence on wavelength, whereasred gingival reflects blue light more poorly than red light as also canbe seen by comparing FIGS. 4(a) and 4(c).

The advantage of the embodiment in FIG. 3 is the relatively small numberof physical elements, but the disadvantage is the loss of power of lightavailable to excite fluorescence, as the light emitted by the singlelight source has to pass through the pattern, i.e., a partly blockedpathway.

All other elements in FIGS. 2 and 3 and the modes of operation enabledby the embodiments illustrated in FIGS. 2 and 3 are as described forFIG. 1 .

Note that in all embodiments, it is not a requirement to know themagnitude of fluorescence perfectly well. In the stitching algorithm, wethe weights are only used to express some level of certainty in theclassification into hard and soft dental tissue, resp. The weights canbe raw values as recorded (for example, intensity or A_(f)), but theycan also be a function of those, for example some categorization ornon-linear function. This invention recognizes that perfect separationof signals into reflection and fluorescence is not possible in practiceand hence is robust to this imperfection.

Although some embodiments have been described and shown in detail, theinvention is not restricted to them, but may also be embodied in otherways within the scope of the subject matter defined in the followingclaims. In particular, it is to be understood that other embodiments maybe utilized and structural and functional modifications may be madewithout departing from the scope of the present invention.

In device claims enumerating several means, several of these means canbe embodied by one and the same item of hardware. The mere fact thatcertain measures are recited in mutually different dependent claims ordescribed in different embodiments does not indicate that a combinationof these measures cannot be used to advantage.

A claim may refer to any of the preceding claims, and “any” isunderstood to mean “any one or more” of the preceding claims.

It should be emphasized that the term “comprises/comprising” when usedin this specification is taken to specify the presence of statedfeatures, integers, steps, or components but does not preclude thepresence or addition of one or more other features, integers, steps,components, or groups thereof.

The features of the method described above and, in the following, may beimplemented in software and carried out on a data processing system orother processing means caused by the execution of computer-executableinstructions. The instructions may be program code means loaded in amemory, such as a RAM, from a storage medium or from another computervia a computer network. Alternatively, the described features may beimplemented by hardwired circuitry instead of software or in combinationwith software.

REFERENCES

-   Amaechi B T, and Higham S M: Use of Quantitative Light-induced    Fluorescence to monitor tooth whitening. In: Lasers in Dentistry    VII, Peter Rechmann, Daniel Fried, Thomas Hennig, Editors,    Proceedings of SPIE Vol. 4249 (2001), pp. 157-162.-   Angmar-Månsson B and ten Bosch J J: Quantitative light-induced    fluorescence (QLF): a method for assessment of incipient caries    lesions. Dentomaxillofacial Radiology (2001) 30, pp. 298-307.-   Callieri M, Cignoni P, Scopigno R. Reconstructing textured meshes    from multiple range+rgb maps. VMV 2002, Erlangen, Nov. 20-22, 2002.-   Hartles R L and Leaver G: The Fluorescence of Teeth under    Ultraviolet Irradiation. Biochemical Journal, vol. 54, no. 4, pp.    632-638.-   Kronfeld T, Brunner D, and Brunnett G: Snake-Based Segmentation of    Teeth from Virtual Dental Casts. Computer-Aided Design &    Applications, 7(2), 2010, 221-233.-   Sinyaeva M L, Mamedov A A, Vasilchenko S Y, Volkova A I, and    Loschenov V B: Fluorescence Diagnostics in Dentistry. Laser Physics,    Vol. 14, No. 8, 2004, pp. 1132-1140.

EMBODIMENTS

-   -   1. A 3D scanner system for detecting and/or visualizing        cariogenic regions in teeth based on fluorescence emitted from        said teeth, said 3D scanner system comprising:        -   an illumination unit capable of providing probe light for            illuminating the teeth, where said probe light comprises            light at a first wavelength which is capable of exciting a            fluorescent material of the teeth;        -   an image sensor for recording images of light received from            the illuminated teeth, where said image sensor is capable of            detecting fluorescence emitted from said fluorescent            material when this is excited by light at said first            wavelength;        -   data processing means configured for:            -   i. creating a digital 3D representation of the 3D                topography of the teeth based on recorded images                comprising probe light reflected from the teeth;            -   ii. creating a representation of the fluorescence                emitted from the fluorescent material of the teeth based                on recorded images comprising the emitted fluorescence,                and            -   iii. mapping the representation of the emitted                fluorescence onto the corresponding portion of the                digital 3D representation of the teeth to provide a                combined digital 3D representation; and        -   a visual display unit on which the combined digital 3D            representation is visualized.    -   2. The 3D scanner system according to embodiment 1, wherein the        image sensor is capable of detecting light at said first        wavelength, and wherein the digital 3D representation of the        teeth is created based on light at the first wavelength in said        images comprising probe light reflected from the teeth.    -   3. The 3D scanner system according to embodiment 1 or 2, wherein        the probe light comprises light at a second wavelength and the        image sensor is capable of detecting light at said second        wavelength, and where the digital 3D representation of the teeth        is created based on light at the second wavelength in said        images comprising probe light reflected from the teeth.    -   4. The 3D scanner system according to any of the previous        embodiments, wherein the illumination unit is configured to        provide light only at the first wavelength or only at the second        wavelength at any time.    -   5. The 3D scanner system according to any of the previous        embodiments, wherein the representation of the fluorescence is a        2D representation and said mapping comprises folding the 2D        fluorescence representation onto the digital 3D representation        of the teeth.    -   6. The 3D scanner system according to any embodiments 1 to 4,        wherein the representation of the fluorescence is a 3D        representation and said mapping comprises registering the 3D        fluorescence representation onto the digital 3D representation        of the teeth.    -   7. The 3D scanner system according to any of the previous        embodiments wherein the emission spectrum of said illumination        unit is predominantly below 500 nm.    -   8. The 3D scanner system according to any of the previous        embodiments, wherein the first wavelength is within the range of        375 nm to 435 nm, such as in the range of 385 nm to 425 nm, such        as in the range of 395 nm to 415 nm, such as in the range of 400        nm to 410 nm.    -   9. The 3D scanner system according to any of embodiments 3 to 8,        wherein the second wavelength is within a range of 500 nm to 850        nm.    -   10. The 3D scanner system according to any of the previous        embodiments, wherein the color image sensor comprises a color        filter array comprising a number of filters allowing light at        said first wavelength to pass and a number of filters allowing        the emitted fluorescence to pass, and where the data processing        means bases at least part of the creating of the digital 3D        representation of the teeth and at least part of the creating        the representation of the fluorescence on the same recorded        images.    -   11. The 3D scanner system according to any of the previous        embodiments, wherein the representation of the emitted        fluorescence is created by analyzing recorded images to identify        sections of these images which correspond to fluorescence        emitted from the teeth.    -   12. The 3D scanner system according to any of the previous        embodiments, wherein the 3D scanner system comprises a dichroic        mirror configured for having a larger reflection coefficient at        said second wavelength than at wavelengths corresponding to the        first wavelength and the fluorescence, and wherein the dichroic        mirror is arranged such that it guides light from the second        light source towards the field of view of the scanner system and        allows fluorescence received from the field of view to pass        towards the image sensor.    -   13. The 3D scanner system according to any of the previous        embodiments, where the field of view for recording the images        comprising probe light reflected from the teeth and for        recording the images comprising the emitted fluorescence, are        substantially identical.    -   14. The 3D scanner system according to any of the previous        embodiments, wherein the illumination unit, the image sensor and        at least one unit of the data processing means are integrated        parts of a handheld 3D scanner device of the 3D scanner system.

1. (canceled)
 2. A 3D scanner system for scanning a surface of teethwithin an oral cavity, the 3D scanner system comprising: a hand-held 3Dintraoral scanner configured to operate with one or more image sensors,the 3D intraoral scanner comprising: i. one or more image sensors; ii. afirst light source configured to emit light at a first wavelength orrange of wavelengths, wherein the intraoral scanner is configured torecord data for a 3D surface topography of the teeth based on lightdetected at the first wavelength or range of wavelengths; iii. a secondlight source configured to emit light at a second wavelength or range ofwavelengths, wherein the second wavelength is in the range of 500 nm to850 nm, wherein the intraoral scanner is configured to record data for acariogenic region based on light detected at the second wavelength orrange of wavelengths; and iv. a tip configured for being mounted over adistal end of the 3D intraoral scanner, said tip comprising a regionwhich is transparent to light emitted by the first and/or second lightsource; one or more processor units operably connected to the hand-held3D intraoral scanner, the one or more processor units configured for: i.shifting between the first and second light sources repeatedly such thatthe surface of the teeth within the oral cavity is illuminatedsuccessively by the light from the first and the second light source;ii. generating a digital 3D representation of the teeth based on therecorded data for the 3D surface topography; and iii. identifying one ormore cariogenic regions in which carries is present based on lightdetected at the second wavelength or range of wavelengths; a displayconfigured for visualizing the digital 3D representation of the teethand/or for visualizing the cariogenic region(s).
 3. The 3D scannersystem according to claim 2, wherein the image sensor(s) are configuredfor detecting light at a wavelength range of 400 nm to 850 nm.
 4. The 3Dscanner system according to claim 2, wherein the image sensor(s) arearranged to capture light within the same field of view of the 3Dintraoral scanner.
 5. The 3D scanner system according to claim 2,wherein the first wavelength is in the range of 250 nm to 500 nm.
 6. The3D scanner system according to claim 2, wherein the 3D scanner system isconfigured for generating a digital representation of the cariogenicregion(s) based on the recorded data for the cariogenic region(s). 7.The 3D scanner system according to claim 6, wherein the 3D scannersystem is configured for mapping the digital representation of thecariogenic region(s) onto the digital 3D representation of the teeth toprovide a combined digital 3D representation.
 8. The 3D scanner systemaccording to claim 7, wherein the cariogenic region(s) are representedwith a distinct color and/or brightness in the combined digital 3Drepresentation.
 9. The 3D scanner system according to claim 2, whereinthe display is configured for visualizing the digital 3D representationof the teeth and the digital representation of the cariogenic region(s).10. The 3D scanner system according to claim 2, wherein the cariogenicregion(s) are arranged according to their true position on the teeth inthe visualization.
 11. The 3D scanner system according to claim 2,wherein the recorded data for the cariogenic region(s) includessub-surface reflection(s) from the teeth.
 12. The 3D scanner systemaccording to claim 2, wherein the tip comprises a mirror configured tofold a beam path of light towards the surface of the oral cavity beingscanned.
 13. The 3D scanner system according to claim 2, wherein thefirst or second light source is mounted near the front of the tip of thehand-held 3D intraoral scanner.
 14. The 3D scanner system according toclaim 2, wherein the 3D scanner system is configured for employing focusscanning when recording the data for the 3D surface topography of theteeth.
 15. The 3D scanner system according to claim 2, wherein the 3Dscanner system is configured for employing triangulation when generatingthe digital 3D representation of the teeth.
 16. The 3D scanner systemaccording to claim 2, wherein the 3D scanner system comprises a controlunit configured for controlling which of the first and the second lightsources provide light at a given time.
 17. The 3D scanner systemaccording to claim 16, wherein the control unit is configured forsequentially turning on/off the first and second light sources in such amanner that only one of these light sources provides light at any time.18. The 3D scanner system according to claim 2, wherein the 3D scannersystem is configured for visualizing the differences in dentin andenamel of the teeth on the digital 3D representation of the teeth. 19.The 3D scanner system according to claim 2, wherein the 3D scannersystem is configured for providing a visual representation of thedigital 3D representation in which dental and enamel of the teeth can bedistinguished by using different colors, textures, or opacities.
 20. The3D scanner system according to claim 18, wherein the 3D scanner systemis configured for generating separate visualizations of the dentin andenamel, wherein said visualizations can be controlled independently byvarying the transparency of the visualizations.
 21. The 3D scannersystem according to claim 19, wherein the 3D scanner system isconfigured for generating separate visualizations of the dentin andenamel, wherein said visualizations can be controlled independently byvarying the transparency of the visualizations.
 22. The 3D scannersystem according to claim 2, wherein the processor unit(s) areconfigured to provide a differentiation between hard and soft dentaltissue in the oral cavity.